Low Peak Amplitudes for Group Additive SynthesisAndrew Horner and Simon Wun 475
Optimizing wavetable synthesis for maximum signal-to-noise ratio should take advantage of manipulating the phase of the components in order to reduce the peak amplitude for a given spectrum. This paper compares various phase selection methods on group additive synthesis, a special case of multiple wavetable synthesis, where each wavetable contains a distinct subset of the harmonics. Group additive synthesis peak factors are up to 30% worse than their counterparts, unless wavetable matching and peak-factor optimization are integrated. The genetic algorithm and simulated annealing methods get the best performance out of both multiple wavetable synthesis and group additive synthesis.

ENGINEERING REPORTS

Reconstruction of Recorded Sound from an Edison Cylinder Using Three-Dimensional Noncontact Optical Surface MetrologyVitaliy Fadeyev, Carl Haber, Christian Maul, John W. McBride, and Mitchell Golden 485
Audio information stored in the undulations of a groove in a mechanical sound carrier, such as a cylinder or disc phonograph record, may be reconstructed, without contact, by measuring the groove shape and position using precision optical metrology methods and digital image processing. This report describes the first three-dimensional reconstruction of recorded sound from a mechanical carrier using this approach. The source material, a celluloid Edison cylinder, was scanned using color-coded confocal microscopy techniques. The results and prospects of this approach are discussed.

Large-Signal Analysis of Class A Vacuum Triode Push-Pull Output StageMuhammad Taher Abuelma'atti 509
A mathematical model of the transfer function of class A push-pull triode vacuum tube amplifiers yields closed-form series expressions for the amplitudes of output spectral components. The results are similar to those of a transistor class A output stage, containing odd-order harmonics and intermodulation components. For small amplitude signals, the degrading components are very small; they monotonically increase with large input tones. The parameters of the model can readily be determined using simple calculations.

Servo Control of Loudspeaker Cone Motion Using an Optical Linear Displacement SensorW. Geiger 518
Large signals in a loudspeaker produce distortion because of nonlinear force factors and changing stiffness. Both effects can be reduced by a classical feedback loop that uses optical means to sense the displacement and cone motion. By sensing the actual location of the cone structure, feedback linearizes the system without requiring a detailed model to precompensate for nonideal mechanical properties. In addition, the feedback system can improve the magnitude and phase versus frequency.